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Recent developments in the chemistry of homo- and heterometallic clusters of Iron, Cobalt and Nickel triads substituted with alkynes and related ligands are examined. New synthetic procedures, bonding modes and structural arrangements have been found. The old and recent applications of these clusters are discussed.

The synthesis and structural characterization of a new coordination polymer [Pb(OH)]n[Ag(SCN)(CN)]n, formed by an anionic layer [Ag(CN)(μ3-SCN)]nn− linked to the 1D cationic fragment [Pb(OH)]n through a bridging cyanide, is reported. We have obtained a rational combination of the pattern of laurionite-type structures (Pb(OH)X, with X = halogen, SCN) with the 2D hexagonal pattern of the silver thiocyanate. The title compound shows luminescent behaviour, and the analysis of the computed band structure allows us to describe the electronic transitions.

The charge density of the hydrated cupric acetate Cu2(μ-OOCCH3)4·2H2O has been studied experimentally at 100 K and by DFT calculations on the isolated molecule using the Quantum Theory of Atoms In Molecules (QTAIMs). The bimetallic moiety is bridged by four equivalent acetate groups each other perpendicular and forming penta-atomic rings. The QTAIM parameters of charge density, its Laplacian, potential and kinetic energy density, delocalization indexes, static deformation density have been used to describe all intra- and intermolecular interactions. The topological analysis of the charge density maps shows the expected bond critical points with the corresponding bond paths, Cu–Cu bonding included. The data obtained using the different parameters and functions are consistent for all types of interatomic interactions, i.e. covalent, dative and intermetallic. The unpaired electrons responsible of the magnetic properties of d9 Cu(II) ions occupy the orbitals pointing towards the acetate groups. The valence shell orbital populations of Cu(II) are consistent with the distortion of the octahedral coordination due to the Jahn–Teller effect.

The synthesis of organometal complexes from chromium hexacarbonyl with 1-methyl-naphthalene ligand is reported. Two arene-chromium-tricarbonyl isomers are formed at competitive yields, featured with the metal fragment coordinated to both the methylated and the benzenic aromatic ring. A single-crystal X-ray diffraction measurement has been performed on the [( η 6 -5,6,7,8,9,10-C 11 H 10 )Cr(CO) 3 ] isomer, which presents the metal carbonyl moiety attached to the benzenic arene ligand. The products of reaction have been studied by UV–VIS–NIR, fluorescence and 1 H NMR spectroscopies. A detailed vibrational characterisation by mean of experimental FT-IR and Raman spectroscopy and DFT calculations is reported. The electron ligand donation to the metal carbonyl system, determined by FT-IR spectroscopy, has been related to the actual decrease of resonance energy of the aromatic hydrocarbon in the complex and compared with other chromium tricarbonyl complexes of different polycyclic aromatic hydrocarbons provided with the naphthalenic moiety.

The reactions of the complexes Fe3(CO)12, H2FeRu3(CO)13, H2Ru4(CO)13 and CpNiRu3(H)3(CO)9 with 2(diphenylphosphino)ethyl-triethoxysilane give considerable yields of the complexes Fe3(CO)10L2 (1), H2FeRu3(CO)10L2 (2), Ru4(CO)10L3 (3) and CpNiRu3(H)3(CO)7L2 (4) where L = Ph2PCH2CH2Si(OEt)3. The complexes (1–3) have been characterized by analytical and spectroscopic techniques. The structure of (4) has been determined by X-ray analysis. The presence of a phosphine containing the –Si(OEt)3 group has been exploited for grafting complexes (3) and (4) on the mesoporous SBA-15 and the resulting inorganic–organometallic materials have been characterized by means of ICP-MS, FT-IR, DR-UV–vis spectroscopy, XRD and textural analysis.

The complex Co2(CO)6[μ-η2-(H3CC CCH2CH2OH)] (1) with the ligand 3-pentyn-1-ol (pol) has been synthesized following established procedures. Its structure has been determined by X-ray analysis. The complex Co2(CO)6(mbo) (mbo = 2-methyl-3-butyn-2-ol, HC CC(CH3)2OH), (3), along with the already known Co2(CO)6(bud) (bud = 1,4-butyn-diol, HOCH2C CCH2OH) (2), and Co2(CO)8 were reacted with 2(diphenylphosphino)ethyl-triethoxysilane [Ph2PCH2CH2Si(OCH2CH3)3] (dpts) and tris(hydroxymethyl)phosphine [P(CH2OH)3] (thp). With dpts, mono- and di-substituted complexes were obtained: these were characterized by analytical and spectroscopic techniques. The structures of Co2(CO)6(dpts)2 (5) and of Co2(CO)4(pol)(dpts)2 (8) have been determined by X-ray analysis. Complex (1) was reacted with 3-(triethoxysilyl)propyl isocyanate [(H3CCH2O)3Si(CH2)3NCO] (tsi): the new complex Co2(CO)6[H3CC CCH2CH2OC( O)NH(CH2)3Si(OCH2CH3)3] (9) was obtained and spectroscopically characterized. The complex has also been reacted with tetraethyl orthosilicate (teos); a new inorganic–organometallic material was obtained. Complex (5) has been grafted on the mesoporous material SBA-15. The hybrid inorganic–organometallic materials obtained have been characterized by inductively coupled plasma-mass spectrometry (ICP-MS), infrared spectroscopy (FT-IR) under vacuum conditions, X-ray diffraction (XRD) and scanning electron microscopy coupled to EDS probe (SEM–EDS).

The reactions of Fe3(CO)12 with 2-methyl-3-butyn-2-ol and 3-pentyn-1-ol in CH3OH/KOH solution lead, respectively, to the binuclear complex Fe2(CO)6(μ-CO)(μ-η2-[HCC{ C(CH3)2}C( O)(OCH3)]) (as the main product) and to the closed trinuclear hydridic complex (μ-H)Fe3(CO)9(μ3-η3-[H3CCC(CH2)(CH2)CO]) (as the unique product). The oxygenated ligands of these complexes are formed, respectively, by coupling of a formerly coordinated CO with a methoxy group and by coupling of a formerly coordinated CO with a deoxygenated alkynic residual.

The thermal reactions of 2-methyl-1-hexen-3-yne [CH3CH2C≡CC(=CH2)CH3, metey] with Fe3(CO)12 have been studied: cluster opening or fragmentation and alkyne dimerization occur. Main products are the open triangular isomers [Fe3(CO)6(μ-CO)2{CH3(=CH2)CC(Et)C(Et)C(=CH2)CH3}] (complex 3a) and [Fe3(CO)6(μ-CO)2{C(Et)CCH3(=CH2)C(Et)CCH3(=CH2)}] (complex 3b). The structure and isomerism of the complexes has been confirmed by X-ray studies. The minor products of the reaction have been characterized by spectroscopic techniques. An attempt at exploiting the reactivity of the “free” C=C bonds of the coordinated ene-yne was made: complex 3a was reacted with styrene under thermal conditions. Unexpectedly considerable yields of the closed triangular cluster [Fe3(CO)6{EtC2C(=CH2)CH3}2] (complex 5) have been obtained. This behaviour had not been previously observed. The unprecedented structure of complex 5 has been confirmed with an X-ray study.

The title complex is the main product of the reaction of Fe3(CO)12 with isopropenylacetylene in basic methanolic solution (followed by acidification); it is obtained upon carbon–carbon bond forming and dimerization of the alkyne. The same complex is also obtained by reacting Fe3(CO)12 in CH3OH/KOH solution with 2-methyl-hex-1-en-3-yne; carbon–carbon bond cleavage presumably occurs to form isopropenylacetylene, which then reacts with the iron carbonyl. The unprecedented structure of the complex has been determined with a X-ray diffraction analysis.

Ru3(CO)12 has been reacted with the compounds hex-1-en-3-yne [EtC≡CCH=CH2], 2-methyl-hex-1-en-3-yne [EtC≡CC(=CH2)CH3] and with 3(ethoxy-silyl)propyl isocyanate [(EtO)3Si(CH2)3NCO] and the compound tb [(EtO)3Si(CH2)3NHC(=O)OCH2C≡CCH2OC(=O)NH(CH2)3Si(OEt)3] in hydrocarbon solution. Some reactions in CH3OH/KOH solution (followed by acidification) have also been performed. The main products of the reactions with ene-ynes are the clusters Ru3(CO)6(μ-CO)2L2 (L = C6H8, C7H10) and their demolition products, the “ferrole” Ru2(CO)6L2 complexes. One of the isomers of Ru3(CO)6(μ-CO)2L2, and Ru2(CO)6L2 (L = C7H10) have been reacted with vinyl-triethoxysilane [(EtO)3SiCH=CH2]: these reactions did not afford complexes containing new carbon–carbon bonds or triethoxy-silyl groups. Only polymerization of vinyl-triethoxysilane occurred. The reactions of Ru3(CO)12 with triethoxysilyl-propyl-isocyanate and tb (in the presence of Me3NO) lead to the same products, that is the isomeric complexes (μ-H)Ru3(CO)9[C=N(H)(CH2)3Si(OEt)3] with a “perpendicular” ligand (complex 3, as proposed on the basis of spectroscopic results) and (μ-H)Ru3(CO)9[HC=N(CH2)3Si(OEt)3] with a “parallel” ligand (complex 4, as confirmed by a X-ray analysis). The reaction pathways leading to these products are discussed. Complex 4 has been reacted with tetraethyl orthosilicate and the resulting material has been characterized. These reactions are part of a study on the synthesis of inorganic-organometallic materials through sol–gel techniques.

Today, the experimental charge density of transition metal compounds can be determined with a good degree of reliability and analyzed with the quantum theory of atoms in molecules in order to better characterize the atomic interaction. Here, we present a short summary of the main topological results obtained with this technique on Mn2(CO)10, Co2(CO)6(μ-CO)(μ-C4O2H2), KMnO4 and KClO4 compounds. To cite this article: R. Bianchi et al., C. R. Chimie 8 (2005).

The title compound has been obtained in considerable yield by reacting Ru3(CO)12 with 2-pentynal-diethyl-acetal [CH3CH2C CC(H)(OEt)2] (PDA) in hydrocarbon solvents. The X-ray analysis shows that the title complex belongs to the well known family of the flyover derivatives. Some X-ray structural studies have been reported, many years ago, on di-iron flyover complexes; in contrast only a few examples of diruthenium derivatives have been structurally characterized. The complex contains ethoxy-groups which could potentially undergo hydrolysis in the presence of tetraethyl-orthosilicate (TEOS) in the presence of catalysts. Reactions of complex Ru2(CO)6[μ-η4-{EtC2C(H)(OEt)2}CO{EtC2C(H)(OEt)2}] with TEOS in the presence of HCl or of NaF (as catalysts) have been attempted. An inorganic-organometallic sol-gel material containing the skeleton of the complex has been obtained and characterized with IR-Raman, XRD on powders and SEM microscopy.

The reactions of Fe3(CO)12 with but-2-yn-1,4-diol (BUD), 1,4-dichloro-but-2-yne (DCB), propargyl alcohol (PA) and propargyl chloride (PC) in KOH/CH3OH solutions (followed by acidification with HCl) and under thermal conditions have been examined. The complex Fe2(CO)6{H2CCCCH2} is the main product of the reactions with BUD or DCB in all conditions. The complexes Fe2(CO)6{H2CCC(H)C(OMe)O} and Fe3(CO)10{H2CCC(H)C(O)C{CH2(O)CH3}CCH2} are the main products obtained respectively in the reactions with propargyl chloride (PC) or propargyl alcohol (PA) in basic methanolic solution. The structures of the three complexes have been determined by means of X-ray analysis. Complex Fe2(CO)6{H2CCCCH2} contains a butatrienyl ligand in an uncommon structural arrangement. The formation of complex Fe2(CO)6{H2CCC(H)C(OMe)O} requires CO and methanol activation; its ferrole like structure contains a coordinated acetate group. Complex Fe3(CO)10{H2CCC(H)C(O)C{CH2(O)CH 3}CCH2} contains one Fe(CO)4 and one Fe2(CO)6 fragments linked through a carbon atom chain derived from the insertion of CO and dimerization of propargyl alcohol (with substitution of OCH3 from methanol in the place of OH). Comments on the syntheses and on the reaction pathways leading to the complexes are made.

The experimental charge density determination ( T = 120 K) of a second-row transition metal cluster and subsequent topological analysis elucidate the bonding of the Ru 3 (CO) 12 molecule. The Ru–Ru bond critical point features were found to be close to those of the first-row transition metal–metal bonds. Furthermore, the experiment reveals the presence of C⋯C interactions among the axial carbonyl ligands. They may justify the sterically hindered D 3h configuration of the molecule and the distortion of axial COs from linearity.

The title complex is obtained by reacting Ru3(CO)12 with 1,4-dichloro-but-2-yne (ClCH2C CCH2Cl, DCB) in CH3OH/KOH solution (followed by acidification with HCl). The X-ray structure analysis shows that (μ-H)2Ru3(CO)9{μ3-η2-[H2C C(H)CCC( O)OCH3]} complex contains a “parallel” ene-yne acetyl substituent, H2C C(H)C CC( O)OCH3; the formation of such a ligand starting from DCB is – to our knowledge – unprecedented. The synthesis of complex (μ-H)2Ru3(CO)9{μ3-η2-[H2C C(H)CCC( O)OCH3]} occurs through the activation of CO and methanol. This process has been found for other reactions of functionalized alkynes with M3(CO)12 carbonyls (M = Fe, Ru) under basic methanolic conditions. The known hydridic cluster, (μ-H)Ru3(CO)9[μ3-η3-(MeCCHCH)] has been identified as the minor reaction product.

Metal–metal bonds belong, from the topological point of view, to the wide class of the closed shell interactions proposed by Bader. Such a simple classification is, however, not satisfying in the description of these bonds and the nature of the metal–metal bond, in particular in polynuclear complexes, is debated. Using some topological and energy parameters, a comparison is made between polynuclear complexes and bulk metals and indicates the similar nature of these bonds.

The thermal reaction of hexacarbonylchromium with the polycyclic aromatic hydrocarbons (PAHs) pyrene, perylene, chrysene and 1,2-benzanthracene has afforded four organometallic complexes of the type [(η6-PAH)Cr(CO)3], whose unprecedented structures were obtained by single-crystal X-ray analysis. The topology of the coordination of the Cr(CO)3 fragment and its asymmetry with respect to the coordinating ring may depend on the opportunity to maintain the maximum aromaticity of the complexed ligand. DFT calculations, 1H NMR, FT-IR and Raman spectroscopy have been used to elucidate the type of interaction between the PAH ligand and the carbonylmetal moiety, giving insight into the ligand-to-metal donor capacity and the intra- and intermolecular interactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The reaction of Ru3(CO)12 with but-2-yn-1,4-diol (HOCH2CCCH2OH, BUD) in CH3OH/KOH followed by acidification with HCl leads to four products, one of which has been identified as the title complex (μ-Cl)Ru3(CO)9[μ3-η4-H2CCC(H)CH2]. This is an open cluster containing a bridging Cl atom on the open side and a C4H5 moiety bound to all the metals. The structure of the complex has been determined by X-ray analysis. The thermal reaction of Ru3(CO)12 with BUD has been revisited for a comparison with the results in alkaline solution. The main product is the allylic derivative HRu3(CO)9[HCCHCCHO].

Ene–yne molecules are found as natural products. Natural and synthetic ene–ynes are actively studied and partly used as anticancer drugs. Conjugated and non-conjugated ene–yne molecules are widely used as synthons in organic reactions promoted by organometallic compounds. Surprisingly, the coordination of ene–ynes to transition metal clusters has not been fully rationalized up to now; the same happens for the (not very many) examples of their reactivity and of their potentials uses. In this paper the synthetic routes leading to (and the structures of) transition metal clusters containing ene–yne ligands are described. Comparisons with the chemistry of di-ynes coordinated to transition metal clusters are made.

The title complex (μ-H)Ru3(CO)9(μ3-η3-C3H3) has been obtained following two different reaction pathways: one is the deamination of diethylaminopropyne, HCCCH2NEt2, in the presence of Ru3(CO)12 under thermal conditions. The other is the reaction of trimethylsilylpropargyl alcohol, (HO)H2CCC(SiMe3) (TSPA), with Ru3(CO)12. The complex is obtained both under thermal conditions and in the reaction of the carbonyl with TSPA in CH3OH/KOH (followed by acidification). Other reaction products, deriving from the loss of Me3Si and of HCHO fragments from TSPA, have also been characterized. Complex (μ-H)Ru3(CO)9(μ3-η3-C3H3) has been spectroscopically characterized and its crystal structure was determined by an X-ray analysis. An isosceles triangle of Ru atoms with an edge bridged by an H atom, is coordinated by an allylic moiety σ-bonded to two Ru atoms and π-interacting with the third Ru atom.

The reaction of Co4(CO)12 with the dipropargylamine [(HCCCMe2)2NMe] (ligand A) leads to moderate yields of the title complex (complex 4). An X-ray analysis has shown that this tetranuclear complex is a ‘spiked’ (or metallo-ligated) triangular cluster containing one molecule of ligand A partially cyclized and coordinated to all four metal atoms. Complex 4 is the first tetracobalt cluster showing this type of structure which was previously found only for two M2Ni2 (M=Fe, Ru) isopropenylacetylene derivatives. Reaction pathways leading to the formation of complex 4 are discussed.

Recent developments in the chemistry of homo- and heterometallic clusters of Iron, Cobalt and Nickel triads substituted with alkynes and related ligands are examined. New synthetic procedures, bonding modes and structural arrangements have been found. The old and recent applications of these clusters are discussed.

The orthorhombic crystal structure of [Co2(CO)6(μ-CO)(μ-C4O2H2)] (1) was determined at 150 K (Fig. 1). Two C−H⋅⋅⋅O bonds connect the molecules, forming waving ribbons along the b axis. The experimental electron density, determined with the aspherical-atom formalism, was analyzed with the topological theory of molecular structure. The presence of the Co−Co bond critical point indicates for the first time the existence of a metal−metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn2(CO)10], confirming our previously established bonding classification for organometallic and coordination compounds.

The reactions of Co2(CO)8 with 1-ethynylcyclohexanol (HCCC6H10OH, ECY) in benzene led mainly to Co2(CO)6(ECY) 1 and to smaller amounts of the methylidyne complex Co3(CO)9[μ3-CCH2(C6H10OH)] 2. The reactions of Fe3(CO)12 with ECY in the same solvent led to binuclear metallacyclic derivatives Fe2(CO)6(ECY)2 (isomers 3a, 3b) or Fe2(CO)6[(ECY)2 − H2O] 3c as the main products; small yields of trinuclear complexes Fe3(CO)9(μ-CO)[μ3-η2-1,2-HCC(C6H10OH)] 4, Fe3(CO)9(μ-CO)[μ3-η2-1,2-CC(C6H10)] 5 and Fe3(CO)7[μ3-η7-(C6H10OH)CCHCHC(C6H9)] 6 {containing respectively a parallel alkynol, an allenylidene and a dimeric metallacyclic ligand} were also obtained, together with 7, a thermal decomposition product of 6. Finally, when Co2(CO)8 was treated with ECY in benzene, and Fe3(CO)12 was added, the heterometallic complex Co2Fe(CO)6(μ-CO)[μ3-η7-(C6H9)CC(H)C(H)C(H)(C6H10)] 8 was obtained in low yields. The complexes have been characterized by means of IR and 1H NMR spectroscopies and by mass spectrometry. The structures of 2, 5, 8 have been determined by X-ray diffraction. Complex 2 contains an “hydrogenated” ECY ligand, 5 an allenylidene ligand formed upon dehydration of ECY (loss of the OH and of the terminal hydrogen), whereas 8 contains a ligand formed by tail-to-tail coupling of two ECY molecules, with loss of water and oxygen and shift of hydrogen. The elemental analysis of complex 8 gave a Co ∶ Fe ratio of 2 ∶ 1; on the basis of this analysis, the refinement of the diffraction data allowed a hypothesis on the distribution of the metal atoms in the cluster. Reaction pathways for the formation of these clusters are proposed and dehydration mechanisms for the ligand discussed.

The compound [Ru3(CO)9[mu-P(NPri2)2]3][Ru6(CO)15(mu 6-C)[mu-P(NPri2)2]] (1), obtained via the addition of PCl(NPri2)2 to K2[Ru4(CO)13], crystallizes in the monoclinic space group P2l/c with a = 15.537(8) A, b = 36.151(16) A, c = 19.407(5) A, beta = 91.14(2) degrees, Z = 4, and R = 0.069 for 8006 observed reflections. The unit cell is unusual in that it contains both a typical octahedral Ru6 cluster anion (1a), featuring an encapsulated carbide, and a symmetrical phosphido bridge, in addition to a 50-electron trinuclear cluster cation [Ru3(CO)9[mu-P(NPri2)2]3]+ (1c). The latter, with approximate D3h symmetry, exhibits long Ru-Ru distances (> or = 3.15 A). Among the family of clusters with M3(mu-PR2)3 cores and different numbers of both electrons (TEC) and terminal ligands (LxLyLz), 1c is unique in that it is a 333 stereotype with 50 valence electrons. MO calculations permit us to predict the existence of redox congeners of 1c clusters and related 48e Re3 clusters. This work also presents a summary of the relationships between the electronic and the geometric structures for all known M3LxLyLz(mu-PR2)3 species. The basic stereochemical features are influenced by the total-electron count and, hence, by the degree of M-M bonding, as well as the remarkable flexibility of the phosphido bridging ligands. The mu-PR2 ligands need not necessarily lie in the M3 plane, and a wide range of M-P-M angles (as small as 72 degrees or as large as 133 degrees) have been observed.

The complexes Co3(CO)9(μ3-X) (X=S, Se) can be reduced to the corresponding anionic species [Co3(CO)9(μ3-X)]−, which react with allyl bromide to give Co3(CO)7(μ-η3-C3H5)(μ3-X) (X=S, Se). These are the first two cobalt complexes containing the bridging μ-η3-allyl ligand. The structure of the selenium complex was determined by X-ray crystallography. Crystal data for Co3(CO)7(μ-η3-C3H5)(μ3-Se) are as follows: space group P21/c, a=9.051(2) A, b=8.102(2) A, c=21.27(4) A, β=93.82(3)°, Z=4, and R=0.0565 for 2491 observed reflections.

The propargyl alcohols RC2C(H)(OH)R′ (R = H, R′ = Et; R = Me, R′ = Et; R = Et, R′ = Me; R = Ph, R′ = Pri) reacted with [Fe3(CO)12] in hydrocarbon solvents to give, as the final products, binuclear “ferrole” derivatives [Fe2(CO)6L2] or [Fe2(CO)6(L)(L − H2O)] [L = propargyl alcohol] in several isomers. Small amounts of tri- and penta-nuclear complexes were also obtained. In particular, when R = H or Ph trinuclear complexes [Fe3(CO)9(μ-CO)L] 1 with a “parallel” alkyne ligand could be isolated and characterized by IR and NMR spectroscopies and mass spectrometry. When R = Me or Et the “bow tie” acetylide complexes [Fe5(CO)14(C2R)2] (R = Me 2a or Et 2b) were isolated; their structures were determined by X-ray diffraction. The complexes 2a and 2b are formed by two Fe3 triangles sharing a common vertex: each triangle is co-ordinated in a perpendicular fashion by an acetylide fragment and the carbon of one of the acetylide ligands is bound to four iron atoms. Complexes 2 are new examples of an uncommon type of cluster framework; they are presumably formed upon condensation of metal fragments generated by triiron dodecacarbonyl and upon cleavage of a carbon–carbon bond α to the alkyne triple bond. Possible formation mechanisms are discussed.

The phosphine-substituted clusters Ru3(CO)9L3 (L=PPh3, 1; L=PEt3, 2) are active homogeneous catalysts for the hydrogenation of diphenylacetylene. In the catalytic reactions involving complex 2, formation of Ru3(CO)10(PEt3)2 (3) has been observed. This complex shows a hydrogenating activity greater than that of the parent complex 2. In the light of these results and of the observed effect of dihydrogen pressure and substrate/cluster ratio, reaction mechanisms are discussed. The structure of 3 has been characterized by X-ray diffraction and is compared with those of other phosphine-substituted triruthenium clusters. Compound 3 crystallizes in the monoclinic space group P21 with a=9.368(7), b=12.20(2), c=13.554(9) A, β=102.63(8)° and Z=2. Refinement of 4975 data gave R1=0.0417 and wR2=0.1105. The two phosphorus ligands occupy equatorial positions on adjacent metal atoms so that they are trans to each other at the ends of the RuRu vector. The presence of bent semi-bridging carbonyl groups makes the molecule chiral and its absolute structure was determined.

Cocrystallization of pyrene with Hg(CN)(2) gives a new clathrate, namely bis[dicyanidomercury(II)] pyrene solvate, [Hg(CN)(2)](2) x C(16)H(10), with molecules of pyrene embedded in cavities of the slightly deformed structure of the mercuric salt; the weak intermolecular N...Hg interactions present in pure Hg(CN)(2) are maintained in the cocrystal. The X-ray analysis of the resulting compound reveals unusual organic-inorganic interactions. One molecule of Hg(CN)(2) lies on a crystallographic mirror plane, while in the other, only the Hg atom is on the mirror plane. The molecule of pyrene is cut by a mirror plane perpendicular to the plane of the molecule.

The paramagnetic Co3(CO)9(μ3−S) cluster (1) reacts with organic compounds containing S−H, S−S, or P−H bonds to give diamagnetic Co3(CO)7(μ-X)(μ3−S) (μ-X = (μ-L, μ-(1,2-η)-L, and μ-(1,3-η)-L) complexes. The reaction was used to prepare the derivatives with μ-L = SR (2a−h; R = Et, t-Bu, CH2Ph, allyl, Ph, C6F5, 2-naphthyl, CH2CH2OH) and PPh2 (7), μ-(1,2-η)-L = P(S)Ph2 (8), and μ-(1,3-η)-L = S2CR (R = SMe (4), OMe (5), Ph (6)). The reaction results in an increase of the oxidation state of cobalt and may be therefore called an oxidative substitution. It is the first successful and rational way to prepare derivatives of Co3(CO)9(μ3-S), a fundamental cluster molecule described in 1961. The crystal structures of the triphenylphosphine-substituted derivative of 2b, Co3(CO)4(PPh3)3(μ-S-t-Bu)(μ3-S) (3), and of 4, 6, and 8 were determined. A new, high-yield synthesis of 1 is described.

The disubstituted clusters[Ir4(CO)10(μ2-LL)] with one edge-bridging ligand have a ground-state geometry with all COs terminal (LL = (MeS)2CHMe, cluster 1) or with three edge-bridging COs (LL = (Ph2P)2CHMe, cluste 2; LL =Ph2P(CH2)3PPh2, cluster 3) in the solid state and in solution. A comparative 13C-NMR study of 1–3 shows that their respective ground-state geometries are merely relative minima of energy in the same kinetic profile of successive fluxional processes consisting of a merry-go-round of six COs about a unique trangular face and the rotation of terminal COs about one Ir-atom. The factors affecting the activation energy of the merry-go-round result from the relative bites of the bidentate ligands in the ground-state geometry, as shown by a comparison of the molecular structures of 2 and 3.

Co2(CO)8 and Te2O react to form the well known Co4(CO)10Te2, Co4(CO)11Te2 complexes and the two new cluster complexes CCo6(CO)12Te2(1), and CCo6(CO)10Te2(Te3) (2). The structures of 1 and 2 were determined by X-ray analysis, together with the triphenylphosphine derivative of 1, CCo6(CO)11(PPh3)Te2(3), which was analyzed to clarify the disordered structure of the parent compound. Complex 1 is formed by a prismatic cluster of cobalt atoms with a carbon embedded in the cage; two tellurium atoms cap the triangular faces of the prism and each cobalt atom links two terminal carbonyl groups. The complex 2 has a similar prismatic cage CCo6; two μ4-Te atoms cap two rectangular faces of the prism, while other two Te atoms bridge two edges of the triangular faces and are linked each other through a third Te atom. Electron counting gives for complex 2 92 electrons: the presence of two long Co–Co distances suggests that the two excess electrons are located on Co–Co antibonding orbitals. Crystal data for 1, space group C2/c, a = 12.845(2) A, b = 13.449(2) A, c = 13.246(2) A, β = 91.95(2)°, Z = 4, R = 0.097 for 2555 reflections; for 2, space group Pnna, a = 17.219(5) A, b= 14.969(6) A, c = 9.178(4) A, Z = 4,R = 0.037 for 3103 reflections; for 3, space group P21/c, a = 9.288(2) A, b = 14.920(6) A, c = 26.300(9) A, β = 99.99(2)°, Z = 4, R = 0.037 for 4300 reflections. The vibrational analysis of the complex 1 was performed and most of the ν(CO), ν(μ6C–Co), ν(Co–Co) and ν(Co–Co) modes were assigned. The ν(Co–Te) modes were interpreted on the basis of the intermolecular coupling, due to the close contact between neighboring clusters in one distinct direction in the crystal.

A detailed description of the ability of halogen bonding to control recognition, self-organization, and self-assembly in 12 crystal, combining low-temperature X-ray diffraction experiments and theoretical DFT-D and MP2 studies of charge density, is reported. The bond critical point features were analyzed using the bonding ellipsoids, in order to make them more evident and easier to compare. We showed that one-electron potential, in contrast to Laplacian of electron density, allows the electron concentration and depletion regions in the valence shell of the iodine atoms to be revealed. Thus, it was demonstrated as an effective tool for understanding the molecular recognition processes in iodine crystal, describing the mutually complementary areas of concentration and depletion of electron density in adjacent molecules. This finding was also confirmed in terms of electrostatic potential, especially using the concept of a-hole. The tiny features of the electrostatic component of halogen-halogen interactions were also visualized through the superposition of the gradient fields of electron density and electrostatic potential. The general picture provided significant arguments supporting the distinction between Type-I (van der Waals) and Type-II (Lewis molecular recognition mechanism) I center dot center dot center dot I interactions. The energies of these interactions, evaluated on the basis of empirical relationships with bond critical points parameters, have allowed estimating the lattice energy for crystalline I-2, which has been found in reasonable agreement with the experimental sublimation energy.

Al+3-doped (Y,Ca)Ba2Cu3O7−y(YBCO) whiskers have been synthesized using a solid-state reaction technique. These materials are promising candidates for solid-state THz applications based on sequences of Josephson Junctions (IJJs). Alumina addition was systematically varied and the effect of aluminium incorporation on the structure has been investigated using single-crystal X-ray diffraction. Aluminium only replaces Cu atoms in the O–Cu–O–Cu chains and a gradual transition from orthorhombic to tetragonal space group occurs, thus increasing the Al content. A gradual modification of the coordination sphere of the copper site has also been observed. The Ca2+ion substitutes mainly the Y3+ion and also, to a small extent, the Ba2+ion.

The compound [Pd(1,4-thioxane)4](BF4)2·4CH3NO2 crystallizes in the monoclinic space group P21/c with a=9.474(2), b=9.529(5), c=21.945(9) A, β=99.77(3)°, Z=2; final R=0.051 for 4325 observed reflections (Pd, C, S and O anisotropically refined). The thioxane ligands around Pd form a square-planar arrangement, with two nitromethane molecules at a distance of 3.115(2) A occupying sites perpendicular to the square-plane formed by the sulfur-bonding thioxanes giving an overall tetragonal bipyramidal coordination around Pd. Intermolecular exchange of 1,4-thioxane on [Pd(1,4-thioxane)4](BF4)2 in deuterated nitromethane and intramolecular interconversion in the bound ligand have been studied as a function of temperature and pressure by 1H NMR lineshape analysis. The first-order rate constant and activation parameters obtained for the intramolecular process, assigned to sulfur inversion, are as follows: ki298=294±26 s−1, ΔHi≠=61.9±1.9 kJ mol−1, ΔSi≠=+10.2±6.5 J K−1 mol−1, ΔVi≠=+2.7±0.2 cm3 mol−1. The intermolecular process yielded the following second-order rate constant and activation parameters: k2298=920±40 m−1 s−1, ΔH2≠=39.5±0.9 kJ mol−1, ΔS2≠=−55.6±2.8 J K−1 mol−1, ΔV2≠=−9.5±0.3 cm3 mol−1. Second-order kinetics and negative values for the entropy and volume of activation indicate an associative Ia or A exchange mechanism. The reactivity of the analogous Pt2+ compound is estimated using the proposed empirical linear correlation function ΔG≠(Pt)=−32.1+1.92ΔG≠(Pd). The calculated second-order rate constant and free energy of activation are 0.3 m−1 s−1 and 76 kJ mol−1, respectively. This relationship indicates also that the well established reactivity order Pd2+≫Pt2+ could be reversed for better π-accepting ligands than MeNC and that, in this case, five-coordinated species on Pt(II) are more stable than the Pd(II) analogue.

Dicobalt octacarbonyl reacts with an excess of (MeSCS2)2 to form several sulfur-containing cobalt carbonyl derivatives; on addition of PPh3, the complex Co2(CO)2(PPh3)2(1,3-η-S2CSMe)(μ-1,2-η-SCSMe) (1) could be isolated from the reaction mixture. The structure of complex 1 was determined by X-ray crystallography; it contains a methyl dithioformate ligand in which the ligand donates five electrons to the cluster and the CS group is bound perpendicular to the Co2 core.

The complexes [Fe 3 (CO) 9 (µ-CO){CCC(H)Ph }] and [Fe 2 (CO) 6 {Ph(H)CCCHC(OMe)O}] have been obtained in low yields from reaction of 1-phenylprop-2-yn-1-ol with [Fe 3 (CO) 12 ] (‘stabilized’ with methanol), together with other oily derivatives, difficult to characterize. Their solid-state structures have been determined using X-ray diffraction techniques. The first reacts with excess of methanol to form the second. However, the yields of the latter are always low irrespective of the amount of methanol used. Experiments showed that this reaction also occurs on the TLC plates used for the chromatographic separation of the complexes. This behaviour is discussed.

A novel chiral C 3 phosphite P(odag) 3 (odag = 1,2∶5,6-di-O-isopropylidene- α-D-glucofuranoside) has been synthesized on a large scale; when treated with Cu(CO)Cl it gave the cubane [{CuCl[P(odag) 3 ]} 4 ], which is in equilibrium with a dimeric form in solution.

Dicobalt octacarbonyl and perfluoro diphenyl disulfide react to form Co3(μ3-S) (C6F5)(CO)8 (1), an unusual cobalt carbonyl cluster containing an aryl-metal sigma bond. The structure of complex 1 was determined by X-ray crystallography; it crystallizes in triclinic P-1 space group with a = 8.218(2), b = 13.379(2), c = 18.864(2) A, α = 106.96(2), β = 96.91(2), γ = 97.39(2)°. The final R is 0.0376 for 5286 observed reflections (F0>4.0σF0).

The complex (1) has been prepared and its structure determined. Complex1 is the first stable thioether derivative of a metal carbonyl containing only cobalt as metal. It crystallizes in the monoclinic P21/c space group, witha = 13.975( 4 ),b = 11.363( 3 ),c = 14.686(2)A,β = 112.25(2)°,V = 2158.5(7)A3.Z = 4. The solution using direct methods and the anisotropic refinement of all nonhydrogen atoms led toR = 0.039,wR = 0.041 for 3296 reflections with F> 4.0σ(F) Analogous but less stable complexes are formed with 1,6-diphenyl-2,5-dithiahexane and the crown thioether 1,4,7-trithiacyclonane, the latter functioning either as a bidenlate or a tridentate ligand.

The structures of CHI3 and of its adduct with quinoline have been analyzed using X-ray single crystal diffraction at low (106 K, CHI3) and room temperature (adduct CHI3⋅3(C9H7N)). The disorder of the molecule is removed at low temperature and the non centrosymmetric structure in P63 space group allows a deep examination of the halogen bondings in the crystal. The iodine atom clearly shows in the both compounds its electrophilic and nucleophilic behavior. It is noteworthy that when iodoform forms adducts involving the three iodine atoms with Lewis bases, it gives raise to non centrosymmetric crystals, and it is a good candidate for obtaining new materials.

The structural transition at different pressures of a halogen and hydrogen bonded molecular structure (iodoform, CHI3) is described. The pressures analyzed up to sample decomposition are 0.85 GPa (P1RT) and 2.15 GPa (P2RT); also room conditions (P0RT) and low temperature (106 K, P0LT) structures have been reported for comparison. The observed disorder–order phase transition, from P63/m to P63 space group, can be rationalized by the intermolecular interaction analysis. The shortening of the distances among iodoform planes, observed during the compression and the temperature decreasing, determines an ordering of molecular dipoles in a parallel arrangement: this phase transition causes a shortening of I⋯I halogen bondings. The BSSE corrected cohesive energies have been calculated for all structures at DFT/B3LYP level of theory using a periodic boundary condition code and the Grimme dispersion correction. Hirshfeld surfaces and electrostatic potential mapped on charge density isosurfaces have been computed and their features have been analyzed, in order to better understand the halogen intermolecular interactions that control the structural modification of iodoform crystal.

The synthesis of homoleptic 1,2:5,6- di -O- isopropylidene -α- d - glucofuranose (HL) complexes bound to metal triple bond moieties was achieved by their reaction with the corresponding molybdenum and tungsten dimethylamido derivatives. The products [Mo2L6] (1) and [W2L6] (2) were characterized by 1H, 13C NMR and IR spectroscopy; optical rotation values were measured and are briefly discussed. The X-ray structures of 1 and 2, determined at 118 and 293 K, respectively, are reported. Crystallographic details: [Mo2L6], monoclinic, space group P2 1 , a = 14.448(11), b = 21.749(12), c = 15.819(9) A , β = 115.07(5)°, Z = 2 and R = 0.0391 for 13 367 independent reflections; [W2L6], orthorhombic, space group P22 1 2 1 , a = 15.993(2), b = 16.127(3), c = 19.260(4) A , Z = 2 and R = 0.067 for 6215 independent reflections.